Some printheads, for example inkjet printheads, comprise a reservoir containing printing fluid with particles in suspension, and a nozzle plate with a plurality of nozzles for ejecting printing fluid from the reservoir towards a printing substrate. Furthermore, in some large format printing apparatus each of the printheads is connected to a tank of printing fluid, which maintains the reservoir of the printhead supplied with printing fluid.
Some printing fluids, such as for example white inks, some metallic inks, or magnetic inks, comprise particles of pigment or additives which tend to precipitate. Maintenance processes, such as spitting, priming or constant recirculation of printing fluid in and out of the printheads, may be implemented when printheads for such printing fluids are not in use, in order to prevent the particles from depositing on the nozzles.